Many machines with moving components are subject to vibration. For example, when a machine including a cantilevered beam moveable in space relative to a stationary frame (such as a gantry robot) is abruptly stopped and started, the beam will undergo transient vibrations due to its inertia and inherent flexibility. In cases where there is a machine tool mounted on the beam for performing useful work, vibration of the beam can be translated into unwanted vibration of the machine tool. This, of course, may be translated into poor work quality and/or having to slow the manufacturing process to allow time for such transient vibrations to settle.
Various methods have been used in an attempt to reduce vibration in machines having moveable components, such as robots. For example, joint sensors have been used to determine position and overshoot of the various drive motors and thereby the position and overshoot of robot arms. The drive motors are then appropriately driven by a feedback control method to attempt to minimize system vibration. Such systems which attempt to control vibration via actuation of the drive motors tend to be costly. Generally, this is because in order to achieve the responsiveness needed, very costly drive motors must be utilized. Moreover, these systems may not very effective because the response of the motors, in many cases, is not sufficient to control transient overshoot vibrations. Moreover, such systems may tend to wear significantly over time.
Several prior references are generally directed towards inertial actuators and controlling vibration in pipes or machines. For example, U.S. Pat. No. 5,209,326 to Harper entitled "Active Vibration Control" teaches attaching inertial actuators to a pipe 23 to control vibration caused by a vibrating diesel engine in communication with the pipe. The control utilized is a feedforward algorithm that takes a signal 31 from the diesel engine and signals from sensors 27, 28 to produce output signals to drive inertial actuators 15. U.S. Pat. No. 5,251,863 to Gossman et al. entitled "Active Force Cancellation System" teaches a system for controlling vibrations in machines whereby an inertial actuator 4 is secured to a flexible foundation 3, collocated with a sensor 5, and aligned along the line of action of the disturbance (the vibrating machinery 1). U.S. Pat. No. to Stetson entitled "Self Tuning Motion/Vibration Supression System" teaches a sensor 32 and proof mass actuator 52 preferably collocated on a mast 26. The proof mass actuator 52 is vibrated according to an "integrated motion energy signal" to maintain the integrated signal of the mast at a minimum. U.S. Pat. No. to Forward et al. describes "Wideband Electromagnetic Damping Of Vibrating Structures." The system includes a sensor 201 for sensing vibration of the structure, a control system 202 and an inertial driver 203 for providing damping forces to damp vibration in the structure. The control utilizes the sum of velocity and acceleration as feedback. Accordingly, none of the above-mentioned patents are directed to systems where the vibrating component undergoes gross motions and transient vibrations resulting therefrom. U.S. Pat. No. 5,102,289 to Yokoshima et al. entitled "Damper Device For Precision Assembling Robot" teaches attaching a passive damper device at the end of the robot arm to absorb vibrations thereof. This systems however, is only effective at a singular frequency and is therefor inefficient in systems where the arm length changes. Moreover, even in systems with unchangeable length arms, the natural frequency of the system can change when the position of the tip of the arm moves in space. A paper given at the Fifth NASA/DOD Controls-Structures Interaction Technology Conference by Raymond Montgomery et al. entitled "Evaluation of Inertial Devices for the Control of Large, Flexible, Space-based Telerobotic Arms," 1993, describes a system for controlling robot arm vibration by controlling a torque wheel having a reaction mass rotatably mounted thereon. However, such torque motors tend to be expensive, require sophisticated controls, and have a tendency to wear when subjected to such constantly reversing loading.
Therefore, there is a long felt, and unmet, need for a simple, rugged and cost effective vibration-damped machine and method where such machines include a beam moving in space relative to a stationary frame, thereby desirably increasing quality and/or manufacturing throughput.